This application is related to Japanese Patent Application No. 2000-027222 filed on Jan. 31, 2000, the entire contents of which are incorporated by reference.
1. Field of the Invention
The present invention relates to an antenna device to be used for portable communication sets.
2. Discussion of the Background
Although a linear antenna such as a pole antenna or a rod antenna has been used in communication sets (e.g., a portable phone), the linear antenna hinders the communication set from being small in size because the antenna is attached at an outside of the case of the communication set. The linear antenna is also likely to break, deform and deteriorate due to external mechanical forces applied to the linear antenna. In addition, the linear antenna is not preferable for reducing the packaging cost because a number of components are required to pack the antenna via coaxial cables and connectors.
For solving the problems described above, Japanese Unexamined Patent Application Publication No. 9-64627 proposes a compact antenna capable of surface-packaging on a circuit board as shown in FIG. 26. A helical antenna is formed within a ceramic substrate 30 by making use of a technique for forming a multi-layer ceramic substrate. A conductor line 31 is formed on each ceramic layer, and the conductor lines on different ceramic layers are connected to one another via through holes 32 in which a conductive material is filled to form a helical conductor as a whole. A ceramic antenna including the helical radiation conductor is assembled by laminating the ceramic layers. A terminal 33 for feeding electricity to the helical conductor is provided on the side face of the substrate 30.
However, because the laminated ceramic sheets are fired after a conductor line is formed on each ceramic sheet, the conductor line is designed by taking into consideration a shrinkage of the conductor line due to the firing process. A highly rigid process control is also required to restrict the shrinkage ratio within a prescribed range, thus making it difficult to reduce the production cost.
Even if all the conductor lines are formed on the surface of the already fired ceramic sheet, conductor patterns should nevertheless be formed on at least four faces of a ceramic block having flat surfaces by a method capable of fine control of the conductor pattern such as a printing method, also preventing the production cost from being reduced.
Accordingly, one object of the present invention is to solve the above and other noted problems.
Another object of the present invention is to provide an antenna device designed to reduce production costs.
To achieve these and other objects, the present invention provides an antenna device including a substrate having upper and lower faces, and a pair of side faces on which convex portions and concave portions are alternately formed. The antenna device also includes a helical conductor layer on the upper and lower faces, and on one of the concave portions and convex portions so as to spirally surround the entire substrate.
Preferably, at least one of the convex and concave portions on the side faces serves as a power feed electrode for feeding electricity to the helical conductor layer in the antenna device according to the present invention.
In addition, the antenna device according to the present invention preferably has a layer including at least one of the dielectric material and magnetic material covering at least a part of the helical conductor layer formed on the substrate.
Further, the antenna device according to the present invention includes a helical antenna in which a helical emission conductor is formed on the surface of the ceramic substrate, and the conductor layer on the upper and lower faces of the substrate can be formed by printing. Electrodes can be formed only on the convex portions by a high speed coating method such as a dip method or by using a roll coater for forming the conductive layer on the convex portions on the side face. Using the roll coater enables superior mass-productivity compared to the printing method to be attained for forming the electrode particularly on the convex portion. It is also an advantage of forming the electrode on the convex portion that solder hardly forms solder bridges when the solder is used for connecting the electrode on the convex portion in mounting the antenna device. When the conductive layer is formed in the concave portion on the side face, on the other hand, it can be formed by filling a conductor material in through holes to be described hereinafter, also offering an advantage that the solder bridge is hardly formed. Accordingly, the present invention can make mass-production easy and reduce production costs.
The surface mountable type antenna can also be readily manufactured since the side face convex portions and concave portions themselves on which conductor lines are formed can be utilized as terminal electrodes.
The side face convex portion or the side face concave portion itself may be utilized as a power feed electrode and an earth electrode as described above. Providing a dielectric layer or a magnetic layer so as to cover the helical conductor enables the antenna device to be more compact.
Resonance frequencies of the antenna may largely be distributed in the present invention when the conductor pattern is formed so that the power feed electrode is connected to the earth electrode on the lower face of the substrate making contact with the circuit substrate.
In addition, allowing the power feed electrode to be connected to the earth electrode on the upper face or on the side face can eliminate the drawbacks as described above to enable a highly precise antenna to be constructed.
The present invention also provides a method of making the antenna device.